Microencapsulated bioactive agents and method of making

Abstract

The invention is directed to microcapsules encapsulating an aqueous solution of a protein, drug or other bioactive substance inside a semi-permeable membrane. The microcapsules are formed by interfacial coacervation where shear forces are limited to 0-100 dynes per square centimeter. The resulting uniform microcapsules can then be subjected to dewatering in order to cause the internal solution to become supersaturated with the dissolved substance. This dewatering allows controlled nucleation and crystallization of the dissolved substance. The crystal-filled microcapsules can be stored, keeping the encapsulated crystals in good condition for further direct use in x-ray crystallography or as injectable formulations of the dissolved drug, protein or other bioactive substance.

What is claimed is:  
     
       1. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces at least as great as the turbulent blood flow within a human artery, said membrane comprising a first polymer and a second polymer capable of adhering to said first polymer. 
     
     
       2. The microcapsule of  claim 1  wherein said membrane comprises at least one membrane forming material selected from the group consisting of polymers of glycerol monostearate, glycerol monooleate, glycerol monolaurate, glycerol dioleate, glycerol distearate, other hydrophobic mono- or polyglycerides, waxy polymers of low molecular weight, polyethylene glycol (PEG) 1000-8000, dextran 4000-20,000, polysaccharides of mol. wt. ranging from about 10,000-100,000, polyvinylpyrrolidone (PVP), polyvinyl alcohols, sterols, phospholipids and lecithins. 
     
     
       3. The microcapsule of  claim 1  wherein said interior cavity also contains said bioactive substance in the form of a highly ordered structure. 
     
     
       4. The microcapsule of  claim 3  wherein said highly ordered structure is a crystal. 
     
     
       5. The microcapsule of  claim 4  wherein said crystal substantially fills said interior cavity. 
     
     
       6. The microcapsule of  claim 5  wherein said membrane substantially conforms to the shape of said crystal. 
     
     
       7. The microcapsule of  claim 6  wherein said membrane is resistant to piercing by said crystal. 
     
     
       8. The microcapsule of  claim 1  wherein said membrane is permeable to water and low molecular weight salts but impermeable to said bioactive agent. 
     
     
       9. The microcapsule of  claim 1  wherein said membrane is less than or equal to 1 micron in thickness. 
     
     
       10. The microcapsule of  claim 1  wherein said bioactive agent is a biomolecule selected from the group consisting of proteins, polypeptides and oligonucleotides. 
     
     
       11. The microcapsule of  claim 1  wherein said interior cavity further comprises a hydrophobic phase surrounded by and partially immiscible with said saturated or near-saturated solution of bioactive agent. 
     
     
       12. A composition comprising a multiplicity of the microcapsule of  claim 1  suspended in an aqueous solution having higher osmotic pressure than that of said bioactive agent solution. 
     
     
       13. The composition of  claim 12  wherein said higher osmotic aqueous solution comprises a dewatering agent capable of causing water to be transported through said membrane and out of said interior cavity. 
     
     
       14. The composition of  claim 13  wherein said dewatering agent is a salt or a high molecular weight polymer which is excluded by said membrane. 
     
     
       15. A pharmaceutical composition comprising a pharmacologically effective multiplicity of the microcapsule of  claim 1 , together with a pharmacologically acceptable carrier. 
     
     
       16. The pharmaceutical composition of  claim 15  wherein the average size of said microcapsules is about 1-20 microns. 
     
     
       17. The pharmaceutical composition of  claim 15  wherein the average size of said microcapsules is about 20-300 microns. 
     
     
       18. The pharmaceutical composition of  claim 15  wherein the average size of said microcapsules is greater than about 300 microns. 
     
     
       19. The microcapsule of  claim 1  wherein said bioactive substance is a saturated or nearly saturated solution of a non-aqueous drug in a hydrocarbon solvent and said membrane is hydrophilic. 
     
     
       20. The microcapsule of  claim 1  wherein said membrane is semi-permeable to said bioactive substance. 
     
     
       21. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces at least as great as the turbulent blood flow within a human artery, said membrane comprising a first polymer and a second polymer capable of adhering to said first polymer, and wherein the hydrophilic/lipophilic balance (HLB) of said second polymer is greater than the HLB of said first polymer. 
     
     
       22. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces at least as great as the turbulent blood flow within a human artery, wherein said membrane is about 3-5 microns thick. 
     
     
       23. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces at least as great as the turbulent blood flow within a human artery, wherein said interior cavity also contains said bioactive substance in the form of a highly ordered structure, wherein said highly ordered structure is a crystal, and wherein said highly ordered structure is about 50-2000 microns in size. 
     
     
       24. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces as least as great as the turbulent blood flow within a human artery wherein said membrane comprises a first polymer and a second polymer capable of adhering to said first polymer. 
     
     
       25. The microcapsule of  claim 24  wherein the hydrophilic/lipophilic balance (HLB) of said second polymer is greater than the HLB of said first polymer. 
     
     
       26. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces as least as great as the turbulent blood flow within a human artery wherein said membrane is about 3-5 microns thick. 
     
     
       27. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces as least as great as the turbulent blood flow within a human artery wherein said interior cavity also contains said bioactive substance in the form of a highly ordered structure, wherein said highly ordered structure is a crystal, and wherein said highly ordered structure is about 50-2000 microns in size. 
     
     
       28. A microcapsule comprising an outer membrane surrounding an interior cavity, said interior cavity containing a saturated or nearly saturated solution of a bioactive substance, said microcapsule being capable of withstanding shear forces as least as great as the turbulent blood flow within a human artery, wherein a composition comprising a multiplicity of the microcapsule suspended in an aqueous solution having higher osmotic pressure than that of said bioactive agent solution, wherein said higher osmotic aqueous solution comprises a dewatering agent capable of causing water to be transported through said membrane and out of said interior cavity, wherein said dewatering agent is a salt or a high molecular weight polymer which is excluded by said membrane, and wherein said polymer is transparent to x-ray radiation and/or does not interfere with the x-ray diffraction pattern of said highly ordered structure.